CONCHOLOGIA CESTRICA. 69 



Genus PLANORBIS, GUETTARD, 1756. 



Animal of P. bicarinatus. [W. G. B.] 



Fig, 136, 



Shell, dextral, discoidal ; spire depressed ; whorls 

 numerous, visible on both sides ; aperture crescentic, 

 or transverse-oval ; peristome thin, the upper margin 

 produced. 



Animal, tentacles slender, filiform ; foot short, ovate. 



Sub-genus PLANORBELLA, HALDEMAN, 1842. 



Shell, with few whorls ; aperture campanulate, or ex- 

 panded, prominent 



P. campanulatus, SAY. 



Planorbis campanulatis, Say, Jour. Acad. Phila. F. S., 

 II., 1821. 



Shell, with 4 whorls, longer than wide ; p. 

 spire plane, or nearly so ; body whorl 

 abruptly dilated, near the aperture, sub- 

 campanulate ; umbilicus profound. H. 

 7, W. 17-12, mill., in its greater and less 

 diameters. 



Station, in rivers and ponds. Dela- 

 ware Water Gap, Pennsylvania. 



Sub-genus HELISOMA, SWAINSON, 1840. 



Shell, ventricose ; spire sunk below the body whorl ; 

 whorls few, often angulated. 



